Very high particulate pollution over northwest India captured by a high-density in situ sensor network

Exposure to particulate matter less than 2.5 µm in diameter (PM_2.5) is a cause of concern in cities and major emission regions of northern India. An intensive field campaign involving the states of Punjab, Haryana and Delhi national capital region (NCR) was conducted in 2022 using 29 Compact and Useful PM_2.5 Instrument with Gas sensors (CUPI-Gs). Continuous observations show that the PM_2.5 in the region increased gradually from < 60 µg m^-3 in 6-10 October to up to 500 µg m^-3 on 5-9 November, which subsequently decreased to about 100 µg m^-3 in 20-30 November. Two distinct plumes of PM_2.5 over 500 µg m^-3 are tracked from crop residue burning in Punjab to Delhi NCR on 2-3 November and 10-11 November with delays of 1 and 3 days, respectively. Experimental campaign demonstrates the advantages of source region observations to link agricultural waste burning and air pollution at local to regional scales.